Chapter 24Transition Metals and

Coordination Compounds

2007, Prentice Hall

Chemistry: A Molecular Approach, 1st Ed.Nivaldo Tro

Roy KennedyMassachusetts Bay Community College

Wellesley Hills, MA

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Gemstones

• the colors of rubies and emeralds are both due to the presence of Cr3+ ions – the difference lies in the crystal hosting the ion

Some Al3+ ions in Al2O3 are replaced by

Cr3+

Some Al3+ ions in

Be3Al2(SiO3)6 are replaced by

Cr3+

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Properties and Electron Configuration of Transition Metals

• the properties of the transition metals are similar to each otherand very different tot he properties of the main group metalshigh melting points, high densities, moderate to very hard,

and very good electrical conductors• in general, the transition metals have two valence

electrons – we are filling the d orbitals in the shell below the valenceGroup 1B and some others have 1 valence electron due to

“promotion” of an electron into the d sublevel to fill it form ions by losing the ns electrons first, then the (n – 1)d

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Atomic Size

• the atomic radii of all the transition metals are very similarsmall increase in size

down a column

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Ionization Energy

• the first ionization energy of the transition metals slowly increases across a series

• third transition series slightly higher 1st IEtrend opposite to

main group elements

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Electronegativity

• the electronegativity of the transition metals slowly increases across a seriesexcept for last element in

the series• electronegativity

slightly increases down the column trend opposite to main

group elements

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Oxidation States• often exhibit multiple oxidation states• vary by 1• highest oxidation state is group number for 3B to 7B

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Coordination Compounds• when a complex ion combines with counterions to

make a neutral compound it is called a coordination compound

• the primary valence is the oxidation number of the metal

• the secondary valence is the number of ligands bonded to the metalcoordination number

• coordination number range from 2 to 12, with the most common being 6 and 4

CoCl36H2O = [Co(H2O)6]Cl3

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Coordination Compound

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Complex Ion Formation• complex ion formation is a type of Lewis acid-

base reaction

• a bond that forms when the pair of electrons is donated by one atom is called a coordinate covalent bond

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Ligands with Extra Teeth• some ligands can form more than one

coordinate covalent bond with the metal atomlone pairs on different atoms that are separate

enough so that both can reach the metal

• chelate is a complex ion containing a multidentate ligandligand is called the chelating agent

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EDTAa Polydentate Ligand

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Complex Ions with Polydentate Ligands

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Geometries in Complex Ions

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Naming Coordination Compounds1) determine the name of the noncomplex ion2) determine the ligand names and list them in

alphabetical order3) determine the name of the metal cation4) name the complex ion by:

1) name each ligand alphabetically, adding a prefix in front of each ligand to indicate the number found in the complex ion

2) follow with the name of the metal cation

5) write the name of the cation followed by the name of the anion

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Common Ligands

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Common Metals found in Anionic Complex Ions

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Isomers

• Structural isomers are molecules that have the same number and type of atoms, but they are attached in a different order

• Stereoisomers are molecules that have the same number and type of atoms, and that are attached in the same order, but the atoms or groups of atoms point in a different spatial direction

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Linkage Isomers

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Geometric Isomers• geometric isomers are stereoisomers that differ

in the spatial orientation of ligands

• cis-trans isomerism in octahedral complexes MA4B2• fac-mer isomerism in octahedral complexes MA3B3• cis-trans isomerism in square-planar complexes MA2B2

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Ex. 24.5 – Draw the structures and label the type for all isomers of [Co(en)2Cl2]+

the ethylenediamine ligand (en = H2NCH2CH2NH2) is bidentate

each Cl ligand is monodentate

octahedral

MA4B2

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Optical Isomers

• optical isomers are stereoisomers that are nonsuperimposable mirror images of each other

[Co(en)3]3+

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Ex 24.7 – Determine if the cis-trans isomers of [Co(en)2Cl2]+ are optically active

• draw the mirror image of the given isomer and check to see if they are superimposable

trans isomer identical to its mirror imageno optical isomerism

cis isomer mirror image is nonsuperimposableoptical isomers

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Bonding in Coordination CompoundsValence Bond Theory

• bonding take place when the filled atomic orbital on the ligand overlaps an empty atomic orbital on the metal ion

• explain geometries well, but doesn’t explain color or magnetic properties

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Bonding in Coordination CompoundsCrystal Field Theory

• bonds form due to the attraction of the electrons on the ligand for the charge on the metal cation

• electrons on the ligands repel electrons in the unhybridized d orbitals of the metal ion

• the result is the energies of orbitals the d sublevel are split

• the difference in energy depends the complex and kinds of ligandscrystal field splitting energystrong field splitting and weak field splitting

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Splitting of d Orbital Energies due to Ligands in a Octahedral Complex

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Strong and Weak Field Splitting

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Complex Ion Color

• the observed color is the complimentary color of the one that is absorbed

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Complex Ion Color and Crystal Field Strength

• the colors of complex ions are due to electronic transitions between the split d sublevel orbitals

• the wavelength of maximum absorbance can be used to determine the size of the energy gap between the split d sublevel orbitals

Ephoton = h = hc/ =

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Ligand and Crystal Field Strength

• the strength of the crystal field depends in large part on the ligandsstrong field ligands include: CN─ > NO2

─ > en > NH3

weak field ligands include H2O > OH─ > F─ > Cl─ > Br─ > I─

• crystal field strength increases as the charge on the metal cation increases

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Magnetic Properties and Crystal Field Strength

• the electron configuration of the metal ion with split d orbitals depends on the strength of the crystal field

• the 4th and 5th electrons will go into the higher energy dx2-y2 and dz2 if the field is weak and the energy gap is small – leading to unpaired electrons and a paramagnetic complex

• the 4th thru 6th electrons will pair the electrons in the dxy, dyz and dxz if the field is strong and the energy gap is large – leading to paired electrons and a diamagnetic complex

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Low Spin & High Spin Complexes

paramagnetic

high-spin complex

diamagnetic

low-spin complex

only electron configurations d4, d5, d6, or d7 can have low or high spin

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Tetrahedral Geometry andCrystal Field Splitting

• because the ligand approach interacts more strongly with the planar orbitals in the tetrahedral geometry, their energies are raised

• most high-spin complexes

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Square Planar Geometry andCrystal Field Splitting

• d8 metals

• the most complex splitting pattern

• most are low-spin complexes

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Applications of Coordination Compounds

• extraction of metals from oressilver and gold as cyanide complexesnickel as Ni(CO)4(g)

• use of chelating agents in heavy metal poisoningEDTA for Pb poisoning

• chemical analysisqualitative analysis for metal ions

blue = CoSCN+

red = FeSCN2+

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Applications of Coordination Compounds

• commercial coloring agentsprussian blue = mixture of hexacyanoFe(II) and

Fe(III)inks, blueprinting, cosmetics, paints

• biomoleculesporphyrin ringcytochrome Chemoglobinchlorphyll

chlorophyll

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Applications of Coordination Compounds

• carbonic anhydrase catalyzes the reaction between water and CO2

contains tetrahedrally complexed Zn2+

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Applications of Coordination Compounds

• Drugs and Therapeutic Agentscisplatin

anticancer drug